I think there might be a reason scientists use that term--perhaps to make clear that the water isn't, say, just a flooded river or something; I found this title to an article in Nature magazine: "Molten ice could block Gulf Stream". My guess is that they want a shortcut way of saying, "the temperature rose enough to melt this ice". I tried Onelook, hoping for a science dictionary hit, but no luck. Do we have any geologists handy? stales?

P.S.--Nature wanted me to subscribe in order to read the article (hah--if I won't give the NYT my personal information, why would these people think I'd give them $?!), but I found it here:
http://forests.org/articles/reader.asp?linkid=21783
It doesn't give any explanation for the term.